(a) Field of the Invention
The present invention relates to a driving apparatus of a display device and a method of driving a display device. More particularly, the present invention relates to a driving apparatus changing a frame frequency of the display device, and a method of driving the display device to change the frame frequency of the display device.
(b) Description of the Related Art
Generally, a liquid crystal display (“LCD”) includes two display panels that respectively have pixel electrodes and a common electrode, and a liquid crystal (“LC”) layer disposed therebetween and having dielectric anisotropy. The pixel electrodes are arranged in a matrix shape, and are connected to switching elements such as thin film transistors (“TFTs”) to sequentially receive data voltages by rows. The common electrode may be provided on the same or a different display panel from the pixel electrode, and receives a common voltage. The pixel electrodes and the common electrode, and the LC layer therebetween, form LC capacitors from a circuit perspective, and the LC capacitors are a primary unit for forming a pixel with the switching elements connected thereto.
In the LCD, a voltage is applied to the pixel and common electrodes to generate an electric field on the LC layer, and by controlling the strength of the electric field, transmittance of light that passes through the LC layer is controlled to thus obtain a desired image. In this case, in order to prevent a degradation phenomenon or flickering generated as the electric field is applied in one direction for a long period of time, polarity of data voltages with respect to a common voltage is inverted by frame, row, or pixel.
Generally, input image signals that are input to a signal controller controlling the outputs of the data voltages are divided into two types. That is to say, the input image signals are divided into film image signals such as a movie that is displayed with a frame frequency of about 24 Hz (i.e., the number of frames displayed during 1 second), and general video image signals that are displayed with a frame frequency of about 60 Hz.
Accordingly, film image signals of about 24 Hz are input to the signal controller through a graphics controller with a frame frequency (input frequency) of about 60 Hz, and are appropriately signal-processed to convert the corresponding data voltages to be transmitted to a data driver with a predetermined frame frequency (output frequency).
As described, input image signals such as film image signals and video image signals having the same frame frequency are adapted to a frame rate conversion (“FRC”) technique to improve the images, particularly picture quality of motion pictures, and to adapt techniques such as a frame insert for motion compensation such that the output frequency is not the same as the input frequency.
In this case, the pixel frequency, i.e., the number of pixels displayed during 1 second, is changed in the method of changing the frame frequency. As examples, a film image signal that is displayed at about 24 Hz is changed and output to have a frame frequency of about 72 Hz as an output frequency, and a video image signal that is displayed at about 60 Hz is changed and output to have an output frequency of about 120 Hz.
However, when the frame frequency is changed to an output frequency with a different magnitude, the pixel frequency is also changed.
Firstly, when the pixel frequency is also changed, the charging times of the pixels between the video image signal and the film image signal become different. That is, since the charging time of the pixel is determined by the number of pixel columns displayed during one second (hereinafter referred to as “horizontal frequency”), if the frame frequency is changed, because the horizontal frequency is also changed by the change of the pixel frequency, charging times become different.
Secondly, when the pixel frequency is also changed, because the frequency of the input image signal input that is input into the signal controller that controls the output of the data voltage by appropriately processing the input image signal is proportional to the pixel frequency, if the frame frequency is changed, the frequency of the input image signal is also changed. Generally, when the pixel frequency is abruptly changed, the input image signal is determined as an unstable state, the signal controller is operated in a fail-safe mode, and a predetermined image or a black image is displayed until the pixel frequency is stable. However, when the frame frequency is changed, because the pixel frequency is changed, an abnormal image may be displayed by the change of the frame frequency during the predetermined time regardless of the state of the input image signal.